1. Field of the Invention
The present invention relates to a radial needle bearing of the type which is assembled into an automatic transmission for motive power machines or various types of oil pressure equipment, and functions to support a rotary shaft within a fixed part of a housing, for example, and to control the quantity of a lubricating oil flowing through a bearing portion.
2. Discussion of the Prior Art
The support bearing provided in an oil pump portion of an automatic transmission for motive power machines, e.g., motor vehicles, requires two functions; one to rotatably support the shaft, and the other to control the quantity of a high pressure oil flowing through the support bearing to restrict the oil flowing toward the low part of the oil flow. To this end, a conventional technique constructs the support bearing such that a sliding bearing 3 is provided between the inner surface of a housing 1 and the outer circumferential surface of a shaft 2, as shown in FIG. 14.
The sliding bearing 3 causes a large torque loss when the shaft 2 rotates. The objective of improving the power performance of motive power machines and reducing fuel consumption causes a designer to use a needle bearing in lieu of the sliding bearing, for the support bearing. An excessive quantity of the oil flowing in the shaft extending direction in a general needle bearing hinders the attempt of applying the needle bearing to the support bearing in the present stage of technology in the related field.
In the above circumstances, Japanese Utility Model Laid-Open Publication No. Hei. 1-83920 proposes the needle bearings with the structures as shown in FIGS. 15 and 16. In the first structure of FIG. 15, a seal ring 4, called a floating seal, is provided between the inner surface of an outer ring 5 forming the needle bearing and the outer surface of a shaft 2. The seal ring 4, shaped like a ring as a whole, is made of synthetic resin. The inner diameter of the seal ring 4 is slightly larger than the outer diameter of the shaft 2. The outer diameter of the seal ring 4 is smaller than the inner diameter of the outer ring 5 but larger than the inner diameter of the inward flange 8a. The seal ring 4 is mounted between a retainer 7 holding a needle 6 and an inward flange 8a located downstream in the flow direction of a lubricating oil, inside the outer ring 5.
In a state that the automatic transmission is operating, an oil pressure presses the seal ring 4 thus mounted against the inner side of the inward flange 8a. In this state, a gap 9 is created between the inner edge of the seal ring 4 and the outer circumferential surface of the shaft 2. The oil flows through the gap 9 downstream.
In the second structure of the needle bearing shown in FIG. 16, a seal ring 4a for controlling the flow rate of lubricating oil is shaped like a ring as a whole and like U in cross section. The inner diameter of the seal ring 4a is slightly larger than the outer diameter of the shaft 2. The outer diameter of the seal ring 4a is smaller than the inner diameter of the outer ring 5 but larger than the inner diameter of the inward flange 8a. Inside the outer ring 5, the seal ring 4a is mounted at a location between the needle 6 and the inward flange 8a located downstream in a state that the U-shaped seal ring 4a is opened toward the opposite side of the needle 6.
The conventional radial needle bearings having the above-mentioned structures have still problems to be solved. The problems are follows.
The radial needle bearing with the first structure shown in FIG. 15 can unsatisfactorily restrict the flow of the lubricating oil because it is very difficult to decrease the width of the gap 9 or to increase the length of the gap. The radial needle bearing with the second structure shown in FIG. 16 may restrict the flow of the lubricating oil because the length of the gap 9a between the inner surface of the seal ring 4a and the outer surface of the shaft 2 can be increased to some extent. However, to secure a satisfactory restriction of the oil flow, the seal ring 4a must be considerably elongated. A limited space for receiving the support bearing in the oil pump portion does not allow excessive elongation of the seal ring 4a.